Garden rooms are now the most over-promised, under-specified addition in UK homes. Chelsea Flower Show this week is full of beautifully integrated garden buildings — pavilions, studios, dissolved thresholds — and the inspiration is real. The execution, six months later in a Surrey back garden, often isn’t.

A “garden room” can mean a £9,000 felt-roofed flat-pack from a Sunday-supplement ad, or a £60,000+ architect-detailed structure that adds real value to the house. Same two words with wildly different outcomes.

Here are four things I would tell anyone before they sign anything:

1. Insulation is key.

A garden room with poor insulation is unusable for eight months of the year. Too hot from May to August, too cold from October to March. The cheap end of the market gets this catastrophically wrong — 50mm of PIR if you’re lucky, single-skin walls, an uninsulated floor sitting on ground screws.

What “proper” looks like: 100–150mm insulation in floor, walls and roof, thermal bridges designed out, a warm roof rather than a cold deck. If the company won’t show you a section drawing, please walk away. I have insulated a posh shed for myself, it was ok, but not a space I wanted to spend a lot of time in. It just "did the job" with blankets across my knees in winter and two fans in the summer!

2. Heating it is not optional, and it is not cheap.

A 15m² garden room properly heated through a UK winter is not free. Electric panel heaters will work but will quietly add a few hundred quid a year to your bill. Underfloor electric is more comfortable but adds £3–5k to the build. A small air-source heat pump is the smart long-term answer but needs to be specced in from day one.

If your supplier hasn’t mentioned heating in their quote, they haven’t quoted you a finished building. They’ve quoted you a shed - which might suit you, but be prepared, do your research, or it will be the blanket.....

3. Permitted development is narrower than people think.

The rules people repeat at dinner parties are wrong about half the time, and I myself get confused. So, under permitted development your outbuilding generally needs to be single-storey, under 2.5m at the eaves if within 2m of a boundary, not forward of the principal elevation, and not covering more than 50% of the garden. It cannot be used as primary living accommodation — so no proper bedrooms, no fully-fitted kitchens. Conservation areas, listed buildings, and Article 4 zones throw all of this out.

If anyone tells you “you definitely don’t need planning,” ask them to put it in writing.

4. The aesthetic problem that nobody addresses.

A garden room that doesn’t relate to the main house I think quietly devalues the garden — and sometimes the house. A grey-cladded modern box twenty feet behind a Victorian terrace is a visual mistake that will bother you every time you look out of the kitchen window.

Match a material, echo a roof pitch, make the buildings sisters! Can you use a colour that already exists somewhere on the elevation? The best garden rooms feel like they grew out of the property, not landed in the garden from outer space!

The honest summary

A good garden room is a small, considered building project. It needs proper foundations, proper insulation, proper heating, proper glazing, proper electrical, and — ideally — a designer or architect who treats it as architecture rather than landscaping.

A bad one is a £15,000 garden ornament that you’ll be apologising for in two years. I should know.......I have one I inherited and it drives me nuts, even though its hidden by a fervent grape vine - and don't get me started on that!

20th May 2026 - Garden Rooms: How to Tell a Building From a Shed.

6th May 2026 - Why Your Walls Look Wrong in May